python - SQLalchemy 查询基于排除关系中的项目

Question

我有一张PartyOrganiser(s) 表，一张Contact(s) 表和一张组织好的Party 表(s).

PartyOrganiser 到 Party 是一对多。
PartyOrganiser 到 Contact 是一对多。
Party 到 Contact 是多对多，有关联表。

class PartyOrganiser(db.Model):
    __tablename__ = 'party_organiser'
    id   = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String)
    parties  = db.relationship("Party",    back_populates='party_organiser')
    contacts = db.relationship("Contacts", back_populates='party_organiser')

contact_party_ass_tab = db.Table('contact_party', db.Model.metadata,
    db.Column('party_id', db.Integer, db.ForeignKey('party.id')),
    db.Column('contact_id', db.Integer, db.ForeignKey('contact.id')))

class Party(db.Model):
    __tablename__ = 'party'
    id      = db.Column(db.Integer, primary_key=True)
    details = db.Column(db.String)
    party_organiser_id = db.Column(db.Integer, db.ForeignKey('party_organiser.id'), nullable=False)
    party_organiser = db.relationship("PartyOrganiser", back_populates="parties", uselist=False)
    attendees = db.relationship("Contact", secondary=contact_party_ass_tab, back_populates='intended_parties')

class Contact(db.Model):
    __tablename__ = 'contact'
    id   = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String)
    party_organiser_id = db.Column(db.Integer, db.ForeignKey('party_organiser.id'), nullable=False)
    party_organiser = db.relationship("PartyOrganiser", back_populates="parties", uselist=False)
    intended_parties = db.relationship("Contact", secondary=contact_party_ass_tab, back_populates='attendees')

主要问题:

在语法上，对于一个特定的派对，我想获取与派对组织者相关但尚未参加派对的那些联系人的列表。 IE。称他们为 potential_attendees，我希望将以下内容作为 SQLalchemy 查询样式解决方案:

class Party(db.model):
    ...
    @property
    def potential_attendees(self):
        # get all contacts for the right party_organiser
        sub_query = Contact.query.filter(Contact.party_organiser_id == self.party_organiser_id)
        # then eliminate those that are already attendees to this party..
        return sub_query.difference(self.attendees) # <- pseudocode

子问题:

此配置在 PartyOrganiser、Party 和 Contact 之间具有固有的 3 向约束:各方和与会者只有在共享一个派对组织者。 IE。 PartyOrganiser1 的联系人都不能是 PartyOrganiser2 组织的 Party2 的参加者。对我来说，这是否受上述格式要求的限制并不明显。事实上我相信它不是。我将如何实现此约束？

Answer 1

您可以通过在联接表上使用 NOT EXISTS 构造来查询关系中排除的项目。

@property
def potential_attendees(self):
    sq = db.session.query(contact_party_ass_tab.columns.contact_id).subquery()
    return db.session.query(Contact).filter(
            Contact.party_organiser_id==self.party_organiser_id,
            ~exists().where(sq.c.contact_id==Contact.id)
        ).all()

就您的其他问题而言，您可以通过为 Party.attendees 和 Contact.intended_pa​​rties 添加属性级别验证器并确保添加到这些列表的任何新项目都具有匹配的 party_organiser_id 来对 ORM 级别施加该约束。这是完整的代码

from flask import Flask
from flask.ext.sqlalchemy import SQLAlchemy
from sqlalchemy import exists

from sqlalchemy.orm import validates


app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///:memory:'
db = SQLAlchemy(app)

class PartyOrganiser(db.Model):
    __tablename__ = 'party_organiser'
    id   = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String)
    parties  = db.relationship("Party",    back_populates='party_organiser')
    contacts = db.relationship("Contact", back_populates='party_organiser')

    def __repr__(self):
        return self.name


contact_party_ass_tab = db.Table('contact_party', db.Model.metadata,
    db.Column('party_id', db.Integer, db.ForeignKey('party.id')),
    db.Column('contact_id', db.Integer, db.ForeignKey('contact.id')))

class Party(db.Model):
    __tablename__ = 'party'
    id      = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String)
    details = db.Column(db.String)
    party_organiser_id = db.Column(db.Integer, db.ForeignKey('party_organiser.id'), nullable=False)
    party_organiser = db.relationship("PartyOrganiser", back_populates="parties", uselist=False)
    attendees = db.relationship("Contact", secondary=contact_party_ass_tab, back_populates='intended_parties')

    def __repr__(self):
        return self.name

    @property
    def potential_attendees(self):
        sq = db.session.query(contact_party_ass_tab.columns.contact_id).subquery()
        return db.session.query(Contact).filter(
                Contact.party_organiser_id==self.party_organiser_id,
                ~exists().where(sq.c.contact_id==Contact.id)
            ).all()

    @validates('attendees')
    def validate_attendee(self, key, attendee):
        assert attendee.party_organiser_id == self.party_organiser_id
        return attendee

class Contact(db.Model):
    __tablename__ = 'contact'
    id   = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String)
    party_organiser_id = db.Column(db.Integer, db.ForeignKey('party_organiser.id'), nullable=False)
    party_organiser = db.relationship("PartyOrganiser", back_populates="contacts", uselist=False)
    intended_parties = db.relationship("Party", secondary=contact_party_ass_tab, back_populates='attendees')

    def __repr__(self):
        return self.name

    @validates('intended_parties')
    def validate_party(self, key, party):
        assert party.party_organiser_id == self.party_organiser_id
        return party

db.create_all()

organiser1 = PartyOrganiser(name="organiser1")
organiser2 = PartyOrganiser(name="organiser2")

db.session.add_all([organiser1, organiser2])
db.session.commit()


org1_party1 = Party(name="Organiser1's Party1", party_organiser_id=organiser1.id)
org1_party2 = Party(name="Organiser1's Party2", party_organiser_id=organiser1.id)

org2_party1 = Party(name="Organiser2's Party1", party_organiser_id=organiser2.id)
org2_party2 = Party(name="Organiser2's Party2", party_organiser_id=organiser2.id)

db.session.add_all([org1_party1, org1_party2, org2_party1, org2_party2])
db.session.commit()

org1_contact1 = Contact(name="Organiser1's contact 1", party_organiser_id=organiser1.id)
org1_contact2 = Contact(name="Organiser1's contact 2", party_organiser_id=organiser1.id)
org1_contact3 = Contact(name="Organiser1's contact 3", party_organiser_id=organiser1.id)
org1_contact4 = Contact(name="Organiser1's contact 4", party_organiser_id=organiser1.id)

org2_contact1 = Contact(name="Organiser2's contact 1", party_organiser_id=organiser2.id)
org2_contact2 = Contact(name="Organiser2's contact 2", party_organiser_id=organiser2.id)
org2_contact3 = Contact(name="Organiser2's contact 3", party_organiser_id=organiser2.id)
org2_contact4 = Contact(name="Organiser2's contact 4", party_organiser_id=organiser2.id)

db.session.add_all([org1_contact1, org1_contact2, org1_contact3, org1_contact4, org2_contact1, org2_contact2, org2_contact3, org2_contact4])
db.session.commit()

org1_party1.attendees.append(org1_contact1)
db.session.commit()

print "Potential attendees of org1_party1 ", org1_party1.potential_attendees

print "Attempting to add a contact of a different organiser. Will throw exception"

org1_party1.attendees.append(org2_contact1)

输出(最后检查上面代码最后一行抛出的异常):

In [1]: from exclusion_query import *
/home/surya/Envs/inkmonk/local/lib/python2.7/site-packages/flask_sqlalchemy/__init__.py:794: FSADeprecationWarning: SQLALCHEMY_TRACK_MODIFICATIONS adds significant overhead and will be disabled by default in the future.  Set it to True or False to suppress this warning.
  'SQLALCHEMY_TRACK_MODIFICATIONS adds significant overhead and '
Potential attendees of org1_party1  [Organiser1's contact 2, Organiser1's contact 3, Organiser1's contact 4]
Attempting to add a contact of a different organiser. Will throw exception
---------------------------------------------------------------------------
AssertionError                            Traceback (most recent call last)
<ipython-input-1-4380704ace46> in <module>()
----> 1 from exclusion_query import *